1. Field of the Invention
The present invention is directed to producing a scintillator ceramic for use in a scintillator member for detecting high-energy radiation, for example x-rays, gamma rays and electron beams.
2. Description of the Prior Art
Scintillator members for detecting high energy radiation contain a phosphor that can absorb the high-energy radiation and convert it into visible light. The luminescent emission thereby generated is electronically acquired and evaluated with the assistance of light-sensitive systems such as photodiodes or photomultipliers. Such scintillator members can be manufactured of single-crystal materials, for example, doped alkali halides. Non-single-crystal materials can be employed as powdered phosphor or in the form of ceramic members manufactured therefrom.
Scintillator ceramics consisting of pigment powders of the rare earth oxisulfides that obey the general total formula EQU (M.sub.1-x Ln.sub.x).sub.2 O.sub.2 S
are well-suited for highly sensitive radiation detectors as required, for example, in x-ray computer tomography. In this formula, M stands for at least one element from the group of rare earths and Ln stands for at least one element suitable as an activator from the group of europium, cerium, praseodymium, terbium, ytterbium, dysprosium, samarium and holmium, whereby x can assume a value up to 2.times.10.sup.-1. The scintillator ceramic should have an optical transmission characteristic of translucent through transparent for a high light yield in the conversion of the high-energy radiation, in order to assure a high transmissivity of the luminescent emission within the scintillator member.
Further, a high quantum efficiency is required in the conversion, whereas an excessive afterglow is undesired.
A high transparency of the scintillator member can only be achieved with a high-density ceramic that has optimally low residual porosity. In addition to a crystal anisotropy of the optical refractive index due to non-uniform crystal structure, foreign phase inclusions as well as grain boundaries and, in particular, pores are disruptive for an optimum transmission of the luminescent emission.
German OS 36 29 180 discloses a method for manufacturing a scintillator ceramic of phosphor powders of the rare earth oxisulfides. In this known method powdered scintillator material, which is acquired according to a conventional flux process, is enclosed vacuum-tight in a metal container and is isostatically pressed therein at a temperature from 800.degree. through 1700.degree. C. and a pressure of 50 through 200 Mpa. In order to obtain an optimally high compression of the powdered scintillator material, a compression additive, for example a complex alkali fluoride, is previously added thereto, prior to compression, in a weight proportion up to 10%. A scintillator ceramic is thus obtained that has a residual porosity below 4% by volume, but which still has individual foreign phase inclusions due to the compression additive and therefore does not have an optimum transmission for visible light.
In addition, disadvantages also exist in this known process, since isostatic hot-pressing is technologically complicated and, for example, requires a 200 Mpa high-pressure technique. Further time-consuming and cost-intensive steps are molding the pigment powder in a metal container that is gastight at high-pressure, and the subsequent unmolding (removal) of the scintillator member from the container.